Search Results

An optically accessed, single-cylinder engine capable of operating at both spark ignition and Homogeneous Charge Compression Ignition (HCCI) combustion was used to investigate the difference in the initiation and development of HCCI combustion due to charge stratification, internal Exhaust Gas Recirculation (iEGR) or spark discharge. Natural-light images were acquired to visualise the differences in chemiluminescent structure (i.e. reaction structures) at the early and late stages of formation during HCCI combustion in an attempt to find better ways of controlling HCCI combustion at low and high loads. Regardless of charge stratification, the cycle-to-cycle deviation of autoignition from temporal and spatial repeatability was comparatively small. Flame initiation appeared initially at single or spatially adjacent sites and we did not observe the growth of any new, (i.e. “secondary” in time) reacting ‘islands’ separate from the original sites.

This study measures, during various transients of speed and load, in-cylinder-, intake-/exhaust- (manifold) pressures and engine torque. The tests were conducted on a typical high power-density, passenger car powertrain (common-rail diesel engine, of in-line 4-cylinder configuration equipped with a Variable Geometry Turbocharger). The objective was to quantify the deterioration (relative to a steady-steady condition) in transient Specific Fuel Consumption (SFC) that may occur during lagged-boost closed-loop control and thus propose an engine control strategy that minimises the transient SFC deterioration. The results, from transient characterisation and the analysis method applied in this study, indicate that transient SFC can deteriorate up to 30% (function of load transient) and is primarily caused by excessive engine pumping-loss.

Lean combustion in spark-ignition engines has long been recognised as a means of reducing both exhaust emissions and fuel consumption. However, problems associated with cycle-by-cycle variations in flame initiation and development limit the range of lean-burn operation. An experimental investigation was undertaken in order to quantify the effects of spark energy released and initial flame kernel growth on the cyclic variability of IMEP and crank angle at which 5% mass fraction was burned in a Honda VTEC-E, stratified-charge, pentroof-type, single-cylinder, optically accessed, spark-ignition engine. Simultaneous CCD images of the flame at the spark plug were acquired from two orthogonal views (one through the piston crown and one through the pentroof) on a cycle-by-cycle basis during the first 40 crank angle degrees after ignition timing, for isooctane port injection at an air to fuel ratio of 22, engine speed of 1500 RPM, 30% volumetric efficiency and 40° crank angle spark advance.

Spray characteristics of injectors depend on, among other factors, not only the level of turbulence upstream of the nozzle plate, but also on whether cavitation arises. "Bulk" cavitation, by which we mean cavitation which arises far from walls and thus far from streamline curvature associated with salient points on a wall, has not been investigated thoroughly experimentally and moreover it is quite challenging to predict by means of computational fluid dynamics. Information about the effect of the injector geometry on the formation of bulk cavitation and quantitative measurements of the flow field that promotes this phenomenon in gasoline injectors does not exist and this forms the background to this work. Evolution of bulk cavitation was visualized in two gasoline multi-hole injectors by means of a fast camera.

Measurements are presented of droplet characteristics and air velocity in the cylinder of a 0.36 litre four valve engine, equipped with an sohc VTEC-E valve train and port injection. The results show that injection at crank angles, θinj(s), when the inlet valve is open results in most of the liquid volume flux being in the form of droplets with Sauter mean diameter between 20 and 30 mm which strikes the sleeve up to about 2.5 cm below the exhaust valves, thus generating a locally rich cloud there. The amount of liquid phase gasoline passing through the plane 16 mm below the spark plug gap increases with θinj(s) up to 50 CA after intake TDC and this, together with the crank angle of droplet arrival and vapour generation, controls stratification of the gaseous fuel phase. The optimum injection time is when the fuel-rich cloud is generated so that the tumble vortex convects it to the spark plug at the time of ignition.

A high-swirl, low Compression Ratio (CR), optically accessed engine that was able to produce a stratified charge was used to investigate the differences in HCCI combustion and in the propagation of the autoignition front between a non-stratified and a stratified charge. Furthermore the relevance of charge stratifying an engine using variable injection timing with large temperature inhomogeneities was investigated. The CHEMKIN code and a detailed reaction mechanism were used to simulate the fuel chemistry of ignition and combustion in a low CR engine. The aim of the simulation was to quantify the effect of initial mixture temperature, Ti and A/F ratio on cool flame and main ignition timing and to evaluate the possibility of charge stratifying our engine.

The droplet velocity, size and distributions of iso-octane fuel from single hole and twin jet air-assist injectors have been measured by phase Doppler velocimetry in the pent-roof for two cylinder head designs of firing four-valve engines running at 1500 rpm, together with the airflow during induction and compression. The use of the twin jet air-assist injector together with the introduction of a transfer-passage between the two intake ports of a Honda VTEC-E valve train arrangement resulted in reduction in ISNOx and COV-1mep of the order of half of those with the single hole injector design without a transfer passage. Droplets, for both heads and injectors, having passed the inlet valves, impinged directly onto the sleeve opposite to their entry without striking the exhaust valves and had velocities up to 30 m/s and Sauter mean diameters which varied from 20 to 50pm.